Apparatus and method of determining the tenacity of bonded granular bodies



May 21, 1935- R. 1.. MELTON 2,001,794

APPARATUS AND METHOD OF DETERMINING THE 'IENACLTY OF BONDED GRANULAR BODIES Filed April 30, 1930 Sheets-Sheet l INVENTOR ROMIE. LEE MELTON ifimmu C. Maia a7 ATTORNEY May 21, 1935- R MELTON 2,001,794

APPARATUS AND METHOD OF DETERMINING THE- TLNACITY OF BONDED GRANULAR BODIES Filed April 30. 1950 2 Sheets-Sheet 2 I, i Y I- uimn Y AXIS INVENTOR ROMIE LEE MELTON BY W O'MM mac/ Q7 ATTORN EY Patented May .21, 1935 UNITED STATES PATENT OFFICE APPARATUS AND METHOD OF DETERMIN- ING THE TENACITY F BONDED GRANU- LAB BODIES Application April 30, 1930, Serial No. 448,552

6 Claims. (0!. 265-18) This invention relates to the art of classifying bonded abrasive articles and the like and more particularly to a method of determining the "tenacity" of the bonded structure and the uni- I formity thereof. The term, tenacity as used herein is defined as being that quality of a body by which it resists being pulled or forced apart. Abrasive bodies are regularly made in a variety of grades of tenacity, depending upon the particular work which theyare to do. This range of grades is obtained in artificial abrasives, such as silicon carbide or crystalline alumina by changes in methods of manufacture. For example, various grades or variations in tenacity may be obtained (1), by the use of different bonding materials, (2) by difierent methods of curing, (3) by the use of different proportions of bond and granular abrasive, and (4) by the use of different combinations of abrasive particle sizes. Because of the efi'ect of these variables,

and others, on the tenacity of the finished product, considerable care and skill is required in the manufacture of abrasive articles so that they will have a predetermined degree of tenacity that is best suited for a specific purpose. Therefore, it is desirable to have a simple and reliable method by which the tenacity of finished abrasive bodies can be tested, so that we may determine whether they conform to specifications and whether they are suitable for the particular work for which they are intended. V

The present invention provides a method and means of determining the tenacity of a finished bonded article and the like by measuring successively the forces required to dislodge abrasive particles from the article'when a furrow of given dimensions is cut in a surface of the article, and hence the work used in cutting the given furrow.

The various features employed in the determination of tenacity will best be understood from the following description taken in connection with the accompanying drawings, in which: Figure 1 is an elevation of the machine shown partly in section;

Figure 2 is a section on the line II-II of Figure 1;

Figure 8 is a sectionbn 'Flgure l;

Figure 4 is an isometric view of a modification showing theuse of a recording mechanism;

Figure 5 is a plan view, partly in section of a modification in which a fluid pressure cylinder and recording means replaces the spring dynamometer shown in Figure 1.

the line III-III of Figure 6 is a side elevation, partly in section, of the modification shown in Figure 5; and

Figure 7 is a chart showing a representative curve obtained by means of my method and apparatus as shown in Figure 4 by means of which -5 frame 6, and is movable vertically by means of the internally threaded hand-wheel I. The latter is provided with a reference scale on a hub. The hand lever 8 is adapted to clamp the split end of the upper arm of the frame 6 upon the post 5 and thereby hold the table at a desired position. A key. 9 is mounted in the lower pro- Jecting arm of the frame 8 and engages a keyway It in the post 5 and thereby prevents rotation of the table 2 when its vertical position is being altered by the rotation of hand-wheel I.

The tool 4 is held in vertically adjustable position, with respect to the articleundergoing test, in a tool support 12 mounted on the carriage l3 which is in movable relationship with the table 3. The tool support I 2 is attached to the carriage 13 by means of a pressure responsive device, such as the spring dynamometer I 4 in which the collar IS on the tool support engages one end of a helical spring l6, while the bearing support I! engages the other end. A pointer l8 and a scale I! are provided to indicate the degree of compression of the spring IS.

The carriage I3 is mounted between guide rails 2| and 22 and is capable of horizontal movement through the action of the screw-threaded shaft 23, which is driven at a constant, predetermined speed by the motor 24 by means of the worm 2i and the worm gear 26.

The cutting tool 4 may be of any desired size, shape or material, but it is preferred to use a tool having a square edge and a slight clearance angle at the rear of the cutting edge, said tool being composed of a wear resistant alloy such as sintered tungsten carbide. A diamond point can also be used.

A recording device, such as that illustrated in the modification shown, in Figure 4 may be mounted on the caniage '13, and used to obtain a continuous record of the forces indicated by the spring dynamometer. In this device an arm 21 is mounted on a collar l5 and carries at its outer end a recording instrument such as a pencil 29.

engage the paper 3| and move it at any desired rate.

Another form of dynamometer, shown in Figures 5 and 6, is found particularly useful where a wide range of force indications are desired. Such a device comprises a compression cylinder t2 and piston 43 which taken together replace the helical spring form of dynamometer shown in Figure 1. In this case the tool upon engaging the work actuates the piston 43 and compresses a fluid in the compression cylinder M. This increased pressure is transmitted through the pipe M to the pressure indicating gauge t5 and to'the pressure recording gauge 46 which are rigidly attached to the carriage l3. The increased pressure actuates a piston 38, movement of which is resisted by a helical spring #9. A rod 50 is rigidly attached to the piston 48 and carries at its outer end a recording instrument such as a pencil 5i. A strip of paper 52 is fastened to the table 53 which is rigidly mounted on the guide rail 2 i.

In the device just described the table or plate 53 remains stationary with respect to the guide rail 2| and frame 6. On the other hand the pressure cylinder 62 and recording gauge cylinder 41 are' supported on the carriage l3, which is reciprocated by means of the screw-threaded shaft 23 as indicated in Figure 6.

The operation of the device may be described as follows:

The article 2 to be tested is placed on the table 3 and securely held in place by means of a clamp 54. Then the table is raised by means of the handwheel I until the surface of the test article is at some predetermined/height above the point of the cutting tool 4 and locked in position by the handlever 8. The motor 24!, which drives the testing device, and the motor 35, which drives the recording mechanism are started in proper sequence to secure a synchronized record of force and of the distance through which the tool moves. Rotation of the screw-threaded shaft 23 causes the carriage l3 to move horizontally, carrying the dynamometer I4 and cutting tool d. The movement of the tool is arrested upon its engagement with the specimen, but the carriage it continues to move and causes the spring to compress until the compressing force on the spring is equal to the force required to remove the particles from the path of the tool. The tool then begins to move and. continues to do so (as long as the driving force is applied) to an extent depending upon the resistance encountered. In the event that'greater resistance is encountered, the tool slows down until sufficient stress is built up in the spring to overcome the resistance encountered. The degree of compression of the spring is thus an indication of the force required to break away the abrasive particles from theembedding medium and may be read directly from the scale I9 of from the curve made by the recording mechanism.

The rate of travel of the carriage and hence the rate of cut of the tool point are varied to suit conditions by varying the speed of the screw-threaded shaft 23. This is accomplished by any convenient means such as a variable speed reduction mechanism or a variable speed driving motor.

In order to obtain comparable and consistent results on abrasive articles of different grit sizes,

I vary the size of the cutting tool used and the depth of the channel or groove cut by said tool so that for any grit size there will be approximately the same number of abrasive particles exposed to the gouging action of said tool.

The curve, shown in Figure '7, is typical of a curve recorded on the paper 3| during a testing operation. The X-axis is graduated in linear units which are proportional to the length of the groove, the latter being cut at a constant rate in a face of the abrasive article. The Y-axis is graduated in any desired units, and the ordinates parallel to this axis indicate the force measured by the dynamometer. This curve shows the force required at each instant to drive the tool and also the distance through which the tool is moved. The average force is easily determined and one may calculate the work required to cut a channel of given size and length by measuring the area contained under the curve A B C D and multiplying by a constant whose value depends upon the scales used to indicate the pressure and the length of the groove respectively.

An indication of the power required may also be obtained by connecting an electrical measuring instrument, such as a wattmeter, in the electrical circuit to the driving motor 24 and measuring the electrical energy supplied. The difierence between this reading when the furrow is being cut and that obtained before the tool engages the test article is an indication of the required power, and hence of the tenacity of the test article. It is understood of course that power is work per unit time and that the tool in this method of measurement always gouges out the furrow in approximately the same time.

Where a curve is obtained by the means shown in Figure 4 or Figure 5 and of the sort indicated in Figure '7, variations in the uniformity of the article are shown by the changes in the ordinates of the curve between the points B and C. These points indicate the beginning and end respectively of the portion of the curve corresponding to average conditions of operation of the tool across the abrasive article.

While the description has been confined to the use of my method and apparatus for the testing of abrasive articles, the same method and apparatus may be used for testing the tenacity of refractory shapes and other materials of a granular nature.

I claim:

1. A method of determining the tenacity of bonded granular articles and the like which comprises measuring the work required to make a groove in the surface of saidbody by ploughing or gouging out the material without substantial frictional wear and varying the dimensions of the groove made so that there is a direct proportion between the dimensions of said groove and the size of the granular particles contained in the test article.

2. An apparatus for measuring the tenacity of bonded granular bodies, comprising a gouging tool mounted for gouging a groove of uniform depth in such a body along a non-repeating path, means for adjusting said body in a direction perpendicular to the direction of the gouging operation, means for moving the tool in the gouging operation along a non-repeating path, and means for measuring the force encountered by said tool at each instant of the gouging operation.

3. An apparatus for measuring the tenacity of bonded granular bodies, comprising a tool mounted for gouging a groove of predetermined depth in such a body along a non-repeating path, means for moving the tool in the gouging operation including a yieldable member through which force is transmitted to the tool. a device for indicating the forceexerted on the tool at each point of its path and a device for recording the work performed by the tool in gouging out a groove of given dimensions in a given time.

4. In an apparatus of the class described, a work supporting member, a gouging tool member, driving means for moving one of said members relatively to the other in a rectilineal path in such a direction that a bonded granular article carried on the work supporting member will be gouged to a predetermined depth, means for indicating the force required at each point of the path of the tool to effect such relative movement, and means for indicating the magnitude of such relative movement.

5. Apparatus for measuring the tenacity of bonded granular articles comprising a support adjustable to permit moving the article to be measuring the force required to move said tool.

6. An apparatus for measuring the tenacity of bonded granular articles comprising a gouging tool mounted for gouginga groove of uniform depth in such an article, adjustable means for rigidly mounting such an article whereby a plane surface lies substantially in the plane of the gouging operation, means for moving the said tool toward and across the said plane surface in a non-repeating path to gouge or plough out the said groove in the said plane surface without substantial frictional wear, and means for indicating the forces encountered by the said tool at each point of its travel in the gouging operation.

ROMIE LEE MELTON. 

